1. Field of the Invention
The present invention relates to an electronic wristwatch which has the ability to compute the local time based on cartesian coordinates which are entered through the bezel or GPS unit which acts as a high resolution data entry mechanism. This device is of particular interest to aviators and other professionals.
2. Prior Art
This invention is directed to a method for retrieving the local time adjusted for local observance of daylight savings time at any location on earth by entry of the cartesian coordinates corresponding to that location. In the preferred embodiment, this invention is described in the context of a wristwatch. In order to achieve a system which operates with an extremely high degree of resolution it is necessary to use a high resolution input device. In this respect, previous methods of inputting data into a wristwatch have fallen far short of achieving the necessary resolution to accommodate the entry of cartesian coordinates without resorting to a keyboard. In addition, there are no other known systems which provide the local time at a specified location based on cartesian coordinates.
The crown of the watch has long been used as a means of providing power to the watch through winding, setting the hands of the watch both mechanically and electronically by using small electric pulse generators, entering information into the watch, and changing the mode of operation of the watch. However, the crown is not adaptable to being a high resolution input device as it is extremely small and difficult to maneuver.
For instance, U.S. Pat. No. 5,477,508 discloses a cylinder or thumb wheel which is disposed perpendicular to the normal position of a crown. This thumb wheel is used to scroll through a variety of menus. The speed of thumb wheel rotation controls the speed of scrolling. The desired menu selection is chosen by pressing a button. This provides an inconvenient and hard to access user interface. In U.S. Pat. No. 4,726,687 an analog timepiece with data entry dials is proposed. This illustrates the primary obstacle in creating a complex watch interface which has been the need to use miniature physical controls for the great multiplicity of commands required to be input. The proposed watch overcomes some of these problems by employing a large ring control device connected to an absolute encoder thereby providing a great multiplicity of positions.
Several methods of utilizing capacitive encoding to provide absolute encoding to detect the position of a shaft are known. The primary limitation of these methods, however, is the width of the track for the capacitive pads. When applied to a watch sized encoder, none of the prior art methods use a track less than one-half inch wide. In order to be useful under the bezel of a watch, the track needs to be approximately one-eighth inch wide. The instant invention complies with the spatial requirements of a wristwatch.
Various other methods of implementing absolute encoding, using brushes with multiple tracks or multiple brushes with two tracks currently exist. But the multiple track encoders are too wide to fit under a bezel, and the multiple brush encoders suffer from a low life span. In the proposed invention, a system for absolute encoding is disclosed which uses one track, multiple brushes, and has a very long life span and complies with the spatial requirements of a wristwatch.
Many methods have been proposed to establish and display local time at multiple points on the earth with a watch. Some systems assume the 24 theoretical time zones spaced every 15 degrees around the earth is correct. These methods are inaccurate because over all of the major land masses the time zone borders do not closely trace the longitude lines.
Other watch systems can provide the local time at a number of cities around the world. For example, in U.S. Pat. No. 4,316,272 a system is disclosed whereby a marker can be manipulated to provide the time at a variety of cities displayed around the circumference of the watch face. In another method disclosed in U.S. Pat. No. 4,681,460 an indicator is displayed on the LCD next to the name of a city printed on the bezel and the watch provides the local time at the indicated city. Other list-based approaches have been proposed. However, these list-based systems are limited by the completeness of the lists which often do not accurately account for more remote cities and regions. It is clear that these list-based methods fall far short of providing the accurate local time at any point on earth.
In U.S. Pat. No. 5,408,444 a wristwatch incorporating a GPS system ascertains local time by determining whether the city located nearest the watch at its receiving point is coincident with the city located nearest the preceding receiving point. If they are coincident, the time can be displayed from memory. If not, the city nearest the present receiving point is accessed in memory, and the time of that city is displayed. The disadvantage of this method is that there are a vast number of locations on earth where the nearest major city is not in the same time zone as locations (cities) nearby. The list of known cities in the world is over 254,000 at present. Although select cities can be accounted for in the database, there will be many locations "near" a certain city which are in a different time zone than the city itself. Thus, this system will often provide an inaccurate time. The proposed invention overcomes this problem by accessing time geographically regardless of proximity to a city.